Though it says 'GSD based' it describes DPV1 parameterizing and should also work when using a DTM. As a result the parameters would be available in DigiVis or the Freelance OPC server, not in the controller.

Unfortunately the HART passthrough of AI/AO 845 is different from that of AI/AO 895, for which this feature has been developed. So it might not work with AI 845.

The configuration happens in the DPV1 tab (Parameter dialog). I'm not really sure if its done in the DPV1 tab of a module or the slave.
Maybe it would be best to try to make it work with a GSD based S800 slave with a AI/AO 895, adding a HART object on the Channel. Then once it works, see if it also works with using DTMs.

In the DPV1 tab for the first entry right click on the empty cell in the upper left corner and select "Create Component". Then go to the type cell of this entry and click it to get a list of choices. For the first entry select Slot/Index. Fill in the correct values.
To add the next command select the last line of the previous and again select "Create component". and so on...